JP2005340026A - Electrolyte liquid and battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery capable of improving a cycle property while keeping large capacity, and an electrolyte liquid used for the same. <P>SOLUTION: The battery is composed of a wound electrode body 20 formed by laminating and winding a cathode 21 and an anode 22 through a separator 23. The separator 23 is impregnated with the electrolyte liquid. The electrolyte liquid contains difluorobenzene, trifluorobenzene, tetrafluorobenzene or pentafluorobenzene. By the above, a cycle property is improved while large capacity is kept. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrolytic solution containing fluorinated benzene and a battery using the same.

  In recent years, many portable electronic devices such as notebook portable computers, cellular phones, and camera-integrated VTRs (video tape recorders) have appeared, and their size and weight have been reduced. Accordingly, as a power source for these portable electronic devices, development of a secondary battery that is lightweight and capable of obtaining a high energy density is in progress. As a secondary battery capable of obtaining a high energy density, for example, a lithium ion secondary battery using a material capable of inserting and extracting lithium (Li) such as a carbon material as a negative electrode active material, or a negative electrode A lithium metal secondary battery using metal lithium as an active material is known.

In these lithium ion secondary batteries or lithium secondary batteries, it has been conventionally studied to add various additives to the electrolytic solution in order to improve battery characteristics. As such an additive, for example, hexafluorobenzene has been proposed, and thereby an effect of preventing overcharge is obtained (see, for example, Patent Document 1).
JP-A-7-302614

  However, although hexafluorobenzene can prevent overcharge, the cycle characteristics that have been required in recent years cannot be obtained, and the development of an electrolyte solution that improves the cycle characteristics has been eagerly desired.

  The present invention has been made in view of such problems, and an object thereof is to provide a battery having a high capacity and excellent cycle characteristics and an electrolytic solution used therefor.

  The electrolytic solution according to the present invention contains at least one fluorinated benzene selected from the group consisting of difluorobenzene, trifluorobenzene, tetrafluorobenzene and pentafluorobenzene.

  A battery according to the present invention includes an electrolyte solution together with a positive electrode and a negative electrode, and the electrolyte solution includes at least one fluorinated compound selected from the group consisting of difluorobenzene, trifluorobenzene, tetrafluorobenzene, and pentafluorobenzene. Contains benzene.

  According to the electrolytic solution of the present invention, since at least one kind of fluorinated benzene in the group consisting of difluorobenzene, trifluorobenzene, tetrafluorobenzene and pentafluorobenzene is included, for example, the battery of the present invention When used, the cycle characteristics can be improved while keeping the capacity high.

  In particular, when the content of fluorinated benzene is 0.0001 mass% or more and 0.1 mass% or less for each type of fluorinated benzene contained, a higher effect can be obtained.

  Furthermore, as the negative electrode active material capable of occluding and releasing the electrode reactant, at least one member selected from the group consisting of simple elements, alloys and compounds of metal elements and simple elements, alloys and compounds of metalloid elements is used. In particular, a high effect can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 shows a cross-sectional structure of a secondary battery according to the first embodiment of the present invention. This secondary battery is a so-called lithium ion secondary battery in which the capacity of the negative electrode is represented by a capacity component due to insertion and extraction of lithium as an electrode reactant. This secondary battery is a so-called cylindrical type, and a wound electrode body 20 in which a belt-like positive electrode 21 and a negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. have. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  For example, a center pin 24 is inserted in the center of the wound electrode body 20. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the spirally wound electrode body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

  FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode active material layer 21B is provided on both surfaces of a positive electrode current collector 21A having a pair of opposed surfaces. Although not shown, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil.

  The positive electrode active material layer 21 </ b> B includes a positive electrode material capable of inserting and extracting lithium, which is an electrode reactant, for example, as the positive electrode active material. That is, the capacity of the positive electrode 21 includes a capacity component due to insertion and extraction of lithium as an electrode reactant.

Examples of the positive electrode material capable of inserting and extracting lithium include lithium such as titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), niobium selenide (NbSe ₂ ), and vanadium oxide (V ₂ O ₅ ). And metal sulfides or metal oxides that do not contain. Further, lithium complex oxidation mainly composed of Li _x MO ₂ (wherein M represents one or more transition metals, x is different depending on the charge / discharge state of the battery, and is generally 0.05 ≦ x ≦ 1.10. Examples include things. As the transition metal M constituting the lithium composite oxide, cobalt, nickel, manganese and the like are preferable. Specific examples of such a lithium composite oxide include LiCoO ₂ , LiNiO ₂ , Li _y Ni _z Co _1-z O ₂ (where y and z vary depending on the charge / discharge state of the battery, and generally 0 <y < 1) <0.7 <z <1.02, and a lithium manganese composite oxide having a spinel structure.

  The positive electrode active material layer 21B also contains, for example, a conductive agent, and may further contain a binder as necessary. Examples of the conductive agent include carbon materials such as graphite, carbon black, and ketjen black, and one kind or a mixture of two or more kinds is used. In addition to the carbon material, a metal material or a conductive polymer material may be used as long as it is a conductive material. Examples of the binder include synthetic rubber such as styrene butadiene rubber, fluorine rubber or ethylene propylene diene rubber, or a polymer material such as polyvinylidene fluoride, and one or two or more kinds are used in combination. It is done.

  The negative electrode 22 has, for example, a configuration in which a negative electrode active material layer 22B is provided on both surfaces of a negative electrode current collector 22A having a pair of opposed surfaces. Although not shown, the negative electrode active material layer 22B may be provided only on one surface of the negative electrode current collector 22A. The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

  The negative electrode active material layer 22B includes one or more negative electrode materials capable of inserting and extracting lithium, which is an electrode reactant, for example, as a negative electrode active material. For example, the binder similar to the positive electrode active material layer 21B may be included. That is, the capacity of the negative electrode 22 includes a capacity component due to insertion and extraction of lithium as an electrode reactant.

  Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials, metal oxides, and polymer materials. Carbon materials include artificial graphite, natural graphite, pyrolytic carbons, cokes, graphites, glassy carbons, organic polymer compound sintered bodies, fibrous carbon, activated carbon, carbon blacks, or non-graphitizable carbon Etc. Examples of the coke include pitch coke, needle coke, and petroleum coke. The organic polymer compound sintered body is a carbonized material obtained by firing a polymer material such as phenols or furans at an appropriate temperature. Examples of the metal oxide include iron oxide, ruthenium oxide, molybdenum oxide, tin oxide, and tungsten oxide. Examples of the polymer material include polyacetylene and polypyrrole.

  Examples of the negative electrode material capable of inserting and extracting lithium include simple elements, alloys, and compounds of metal elements or metalloid elements capable of forming an alloy with lithium. These are preferable because a high energy density can be obtained. In particular, when used together with a carbon material, a high energy density can be obtained and excellent charge / discharge cycle characteristics can be obtained. Note that in this specification, alloys include those composed of one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.

Examples of such metal elements or metalloid elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), and cadmium. (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) or hafnium (Hf). It is done. These alloys or compounds, for example, those represented by a chemical formula Ma _s Mb _t. Ma represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, and Mb represents at least one of elements other than Ma. The values of s and t are s> 0 and t ≧ 0, respectively.

  Among them, a simple substance, alloy or compound of a group 14 metal element or metalloid element in the long-period periodic table is preferable, and silicon or tin, or an alloy or compound thereof is more preferable. These may be crystalline or amorphous.

Specific examples of such alloys or compounds include SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi _2. , Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO, LiSnO or Cu—Sn alloy.

  As other alloys or compounds, for example, a lithium-aluminum alloy, a LiAlMe alloy (Me is at least one member selected from the group consisting of group 2 elements, group 13 and group 14 elements in the long-period periodic table) And aluminum-antimony alloy or copper-magnesium-antimony alloy.

  Such an alloy or compound can be obtained by, for example, a mechanical alloying method, a method in which raw materials are mixed and heat-treated in an inert atmosphere or a reducing atmosphere, a melt spinning method, a gas atomizing method, or a water atomizing method.

Furthermore, as the negative electrode material capable of inserting and extracting lithium, other metal compounds or polymer materials can be cited. Examples of the other metal compounds include oxides such as iron oxide, ruthenium oxide, and molybdenum oxide, and LiN _3. Examples of the polymer material include polyacetylene.

  The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 23 is composed of, for example, a porous film made of a synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. The porous film may be laminated.

  The separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. The electrolytic solution contains a solvent and an electrolyte salt dissolved in the solvent.

  Examples of the solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4- Non-aqueous solvents such as methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, acetate ester, butyrate ester, or propionate ester can be mentioned. As the solvent, one kind may be used alone, or two or more kinds may be mixed and used.

Examples of the electrolyte salt include lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiCl, or LiBr. . As the electrolyte salt, one kind may be used alone, or two or more kinds may be mixed and used.

  The electrolytic solution further contains fluorinated benzene. As the fluorinated benzene, for example, difluorobenzene shown in Chemical Formula 1, trifluorobenzene shown in Chemical Formula 2, tetrafluorobenzene shown in Chemical Formula 3, or pentafluorobenzene shown in Chemical Formula 4 is preferable. This is because the cycle characteristics can be improved while keeping the capacity high. In particular, a high effect can be obtained when a single element, alloy or compound of a metal element or a metalloid element is used as a negative electrode material capable of inserting and extracting lithium. These may be used alone or in combination of two or more.

  Specific examples of these fluorinated benzenes include 1,2-difluorobenzene, 1,3-difluorobenzene, and 1,4-difluorobenzene as the difluorobenzene shown in Chemical Formula 1, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene and 1,3,5-trifluorobenzene are exemplified as the trifluorobenzene shown in FIG. Examples thereof include 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, and 1,2,4,5-tetrafluorobenzene. Among them, difluorobenzene is preferably substituted at 1,2, substituted trifluorobenzene is preferably substituted at 1,2,4, and tetrafluorobenzene is substituted at 1,2,4,5. preferable. This is because a high effect can be obtained.

  The content of fluorinated benzene is, for example, preferably 0.0001% by mass or more and 0.1% by mass or less, particularly 0.0001% by mass or more and 0.06% by mass when one kind of fluorinated benzene is contained. % Or less is desirable. Further, when two or more kinds of fluorinated benzenes are contained, it is preferably 0.0001% by mass or more and 0.1% by mass or less for each, particularly 0.0001% by mass or more and 0.06% by mass or less. Is desirable. This is because a high effect can be obtained within this range. In this case, the structural isomer is a different species.

  For example, the secondary battery can be manufactured as follows.

  First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like material. A positive electrode mixture slurry is obtained. Subsequently, the positive electrode mixture slurry is applied to the positive electrode current collector 21A and the solvent is dried. Then, the positive electrode active material layer 21B is formed by compression molding using a roll press or the like, and the positive electrode 21 is manufactured.

  Next, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture slurry. And Subsequently, the negative electrode mixture slurry is applied to the negative electrode current collector 22A, and the solvent is dried. Then, the negative electrode active material layer 22B is formed by compression molding using a roll press or the like, and the negative electrode 22 is manufactured.

  Next, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, the electrolytic solution is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery shown in FIG. 1 is completed.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode active material layer 21B and inserted into the negative electrode active material layer 22B through the electrolytic solution. In addition, when discharging is performed, for example, lithium ions are released from the negative electrode active material layer 22B and inserted into the positive electrode active material layer 21B through the electrolytic solution. At that time, since the electrolytic solution contains difluorobenzene, trifluorobenzene, tetrafluorobenzene or pentafluorobenzene, the cycle characteristics are improved.

  As described above, according to the present embodiment, since the electrolytic solution includes at least a species of the group consisting of difluorobenzene, trifluorobenzene, tetrafluorobenzene and pentafluorobenzene, the cycle is maintained while maintaining a high capacity. Characteristics can be improved.

  In particular, when the content of fluorinated benzene is 0.0001% by mass or more and 0.1% by mass or less for each type of fluorinated benzene contained, higher effects can be obtained.

  Further, when a negative electrode active material capable of occluding and releasing lithium, at least one member selected from the group consisting of simple elements, alloys and compounds of metal elements and simple elements, alloys and compounds of metalloid elements is used. In particular, a particularly high effect can be obtained.

[Second Embodiment]
In the secondary battery according to the second embodiment of the present invention, the negative electrode active material layer 22B has a metal element or a metalloid element as a negative electrode active material capable of inserting and extracting lithium as an electrode reactant. It has the same configuration, operation, and effects as the battery of the first embodiment except that it includes a simple substance, an alloy, or a compound and is formed by a gas phase method, a liquid phase method, or a sintering method. . Therefore, with reference to FIG. 1 and FIG. 2, the same code | symbol is attached | subjected to a corresponding component and description of the same part is abbreviate | omitted.

  In this secondary battery, the negative electrode active material layer 22B is formed by a vapor phase method, a liquid phase method, or a sintering method, so that destruction due to expansion / contraction of the negative electrode active material layer 22B accompanying charge / discharge can be suppressed. At the same time, the anode current collector 22A and the anode active material layer 22B can be integrated, and the electron conductivity in the anode active material layer 22B can be improved. In addition, the binder and voids can be reduced or eliminated, and the negative electrode 22 can be made thin.

  As the vapor phase method, for example, a physical deposition method or a chemical deposition method can be used. Specifically, a vacuum deposition method, a sputtering method, an ion plating method, a laser ablation method, a thermal CVD (Chemical Vapor Deposition) A chemical vapor deposition method) or a plasma CVD method can be used. As the liquid phase method, a known method such as electrolytic plating or electroless plating can be used. As for the sintering method, a known method can be used, for example, an atmosphere sintering method, a reaction sintering method, or a hot press sintering method can be used.

  The negative electrode active material layer 22B is preferably alloyed with the negative electrode current collector 22A in at least a part of the interface with the negative electrode current collector 22A. Specifically, it is preferable that the constituent element of the negative electrode current collector 22A is diffused in the negative electrode active material layer 22B, the constituent element of the negative electrode active material is diffused in the negative electrode current collector 22A, or they are mutually diffused at the interface. The negative electrode active material layer 22B and the negative electrode current collector 22A can be firmly bonded. Even if the negative electrode active material layer 22B expands and contracts due to charge / discharge, the negative electrode active material layer 22B is separated from the negative electrode current collector 22A. This is because dropping off can be suppressed. This alloying often occurs at the same time when the anode active material layer 22B is formed by a vapor phase method, a liquid phase method or a sintering method, but is caused by further heat treatment or during initial charging. But you can.

  The anode current collector 22A is preferably made of a metal material containing at least one metal element that does not form an intermetallic compound with lithium, for example. When an intermetallic compound is formed with lithium, it expands and contracts with charge and discharge, structural destruction occurs, and current collecting performance is reduced. In addition, the ability to support the negative electrode active material layer 22B is reduced, and the negative electrode active material layer 22B becomes a negative electrode. This is because the current collector 22A may fall off. Examples of the metal element that does not form an intermetallic compound with lithium include copper, nickel, titanium, iron, and chromium (Cr).

  The negative electrode current collector 22A preferably contains a metal element that forms an alloy with the negative electrode active material layer 22B. As a metal element that does not form an intermetallic compound with lithium and forms an alloy with the negative electrode active material layer 22B, for example, when using a simple substance, alloy, or compound of silicon or tin as the negative electrode active material, copper, nickel, or iron Etc.

[Third Embodiment]
The secondary battery according to the third embodiment of the present invention is a so-called lithium metal secondary battery in which the capacity of the negative electrode is represented by a capacity component due to precipitation and dissolution of lithium as an electrode reactant.

  This secondary battery has the same configuration and effects as those of the first secondary battery except that the configuration of the negative electrode active material layer 22B is different. Therefore, with reference to FIG. 1 and FIG. 2, the same code | symbol is attached | subjected to a corresponding component and description of the same part is abbreviate | omitted.

  The negative electrode active material layer 22B is made of lithium metal deposited during charging, does not exist during assembly, and dissolves during discharge. That is, in this secondary battery, lithium metal is used as the negative electrode active material, and thereby a high energy density can be obtained.

  This secondary battery can be manufactured in the same manner as the above-described lithium ion secondary battery except that the negative electrode active material layer 22B is formed by charging.

  In this secondary battery, when charged, for example, lithium ions are separated from the positive electrode 21 and deposited as lithium metal on the surface of the negative electrode current collector 22A via the electrolytic solution, as shown in FIG. Then, the negative electrode active material layer 22B is formed. When the discharge is performed, for example, lithium metal is eluted as lithium ions from the negative electrode active material layer 22B, and is occluded in the positive electrode 21 through the electrolytic solution. Here, since the electrolytic solution contains difluorobenzene, trifluorobenzene, tetrafluorobenzene or pentafluorobenzene, the cycle characteristics are improved.

  As described above, in this embodiment, since the electrolytic solution includes at least one selected from the group consisting of difluorobenzene, trifluorobenzene, tetrafluorobenzene, and pentafluorobenzene, lithium metal is used as the negative electrode active material. Even when the capacity of the negative electrode 22 is used in a secondary battery represented by a capacity component due to precipitation and dissolution of lithium, the cycle characteristics can be improved while maintaining a high capacity.

  In the secondary battery, the case where the negative electrode active material layer 22B is formed at the time of charging has been described. However, the negative electrode active material layer 22B may already be provided when the battery is assembled. In this case, similarly to the lithium ion secondary battery, the negative electrode current collector 22A may be provided with the negative electrode active material layer 22B, but the negative electrode active material layer 22B is also used as a current collector, The body 22A may be deleted.

[Fourth Embodiment]
The secondary battery according to the fourth embodiment of the present invention includes a negative electrode having a capacity component due to insertion and extraction of lithium, which is an electrode reactant, and a capacity component due to precipitation and dissolution of lithium. It is represented by.

  In this secondary battery, the open circuit voltage (that is, the battery voltage) is overcharged in the charging process by making the charging capacity of the negative electrode material capable of inserting and extracting lithium smaller than the charging capacity of the positive electrode 21. Except that lithium metal begins to be deposited on the negative electrode 22 at a time lower than the voltage, the rest has the same configuration and effects as the secondary battery according to the first embodiment. Can be manufactured. Therefore, with reference to FIG. 1 and FIG. 2, the same code | symbol is attached | subjected to a corresponding component and description of the same part is abbreviate | omitted.

  The overcharge voltage refers to the open circuit voltage when the battery is overcharged. For example, the safety of lithium secondary batteries is one of the guidelines established by the Japan Storage Battery Industry Association (Battery Industry Association). Refers to a voltage that is higher than the open circuit voltage of a “fully charged” battery as defined and defined in the “Evaluation Criteria Guidelines” (SBA G1101). In other words, it refers to a voltage higher than the open circuit voltage after charging using the charging method, standard charging method, or recommended charging method used when determining the nominal capacity of each battery. For example, when full charge occurs when the open circuit voltage is 4.2 V, the surface of the negative electrode material capable of inserting and extracting lithium in a part of the open circuit voltage in the range of 0 V to 4.2 V Lithium metal is deposited on the surface. Therefore, in this secondary battery, both the negative electrode material capable of inserting and extracting lithium and lithium metal function as a negative electrode active material, and the negative electrode material capable of inserting and extracting lithium is lithium metal. It is a base material for precipitation.

  This secondary battery is the same as the conventional lithium ion secondary battery in that a negative electrode material capable of inserting and extracting lithium is used for the negative electrode 22, and lithium metal is deposited on the negative electrode 22. Is the same as the conventional lithium metal secondary battery, but the lithium battery is deposited on the negative electrode material capable of inserting and extracting lithium, so that this secondary battery can obtain a high energy density. In addition, the cycle characteristics and quick charge characteristics can be improved.

  In this secondary battery, when charged, lithium ions are released from the positive electrode 21 and are first inserted into the negative electrode material capable of inserting and extracting lithium contained in the negative electrode 22 through the electrolytic solution. When charging is further continued, lithium metal begins to deposit on the surface of the negative electrode material capable of inserting and extracting lithium in a state where the open circuit voltage is lower than the overcharge voltage. After that, lithium metal continues to deposit on the negative electrode 22 until charging is completed. Next, when discharging is performed, first, lithium metal deposited on the negative electrode 22 is eluted as ions, and is occluded in the positive electrode 21 through the electrolytic solution. When the discharge is further continued, lithium ions occluded in the negative electrode material capable of occluding and releasing lithium in the negative electrode 22 are released and occluded in the positive electrode 21 through the electrolytic solution. Here, since the electrolytic solution contains difluorobenzene, trifluorobenzene, tetrafluorobenzene or pentafluorobenzene, the cycle characteristics are further improved.

  As described above, in the present embodiment, the electrolytic solution includes at least one selected from the group consisting of difluorobenzene, trifluorobenzene, tetrafluorobenzene, and pentafluorobenzene. Cycling characteristics while maintaining a high capacity even when used in secondary batteries that include a capacity component due to insertion and extraction of lithium, which is a substance, and a capacity component due to precipitation and dissolution of lithium. Can be improved.

[Fifth Embodiment]
FIG. 3 shows a configuration of a secondary battery according to the fifth embodiment of the present invention. This secondary battery is a so-called laminate film type, and has a wound electrode body 30 to which a positive electrode lead 31 and a negative electrode lead 32 are attached accommodated in a film-shaped exterior member 40.

  The positive electrode lead 31 and the negative electrode lead 32 are led out, for example, in the same direction from the inside of the exterior member 40 to the outside, and are each made of a metal material such as aluminum, copper, nickel, or stainless steel.

  The exterior member 40 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. For example, the exterior member 40 is disposed so that the polyethylene film side and the wound electrode body 30 face each other, and the outer edge portions are in close contact with each other by fusion bonding or an adhesive. An adhesive film 41 is inserted between the exterior member 40 and the positive electrode lead 31 and the negative electrode lead 32 to prevent intrusion of outside air. The adhesion film 41 is made of a material having adhesion to the positive electrode lead 31 and the negative electrode lead 32, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 40 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 4 shows a cross-sectional structure taken along line II of the spirally wound electrode body 30 shown in FIG. The wound electrode body 30 is formed by stacking and winding a positive electrode 33 and a negative electrode 34 with a separator 35 and an electrolyte layer 36 interposed therebetween, and the outermost periphery is protected by a protective tape 37.

  The positive electrode 33 has a structure in which a positive electrode active material layer 33B is provided on one side or both sides of a positive electrode current collector 33A, and the negative electrode 34 also has a negative electrode active material layer 34B on one side or both sides of the negative electrode current collector 34A. It has a provided structure. The positive electrode 33 and the negative electrode 34 are disposed so that the positive electrode active material layer 33B and the negative electrode active material layer 34B face each other. The specific configuration of the positive electrode current collector 33A, the positive electrode active material layer 33B, the negative electrode current collector 34A, the negative electrode active material layer 34B, and the separator 35 is the positive electrode current collector according to any one of the first and fourth embodiments. The same as the body 21A, the positive electrode active material layer 21B, the negative electrode current collector 22A, the negative electrode active material layer 22B, and the separator 23.

  The electrolyte layer 36 is configured by a so-called gel electrolyte in which an electrolytic solution is held in a holding body. A gel electrolyte is preferable because it can obtain high ionic conductivity and prevent leakage. The configuration of the electrolytic solution is the same as that of the first embodiment.

  The holding body is made of, for example, a polymer material. As the polymer material, for example, a fluorine-based polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, an ether-based polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, or Examples include polyacrylonitrile. In particular, from the viewpoint of redox stability, a fluorine-based polymer compound is desirable.

  For example, the secondary battery can be manufactured as follows.

  First, after forming the positive electrode 33 and the negative electrode 34 in the same manner as in any of the first to fourth embodiments, the electrolyte layer 36 in which the electrolytic solution is held in the holding body is formed on each of the positive electrode 33 and the negative electrode 34. To do. Next, the positive electrode lead 31 is attached to the end portion of the positive electrode current collector 33A, and the negative electrode lead 32 is attached to the end portion of the negative electrode current collector 34A. Subsequently, the positive electrode 33 and the negative electrode 34 on which the electrolyte layer 36 is formed are stacked via the separator 35, and then wound in the longitudinal direction to form the wound electrode body 30. After that, for example, the wound electrode body 30 is sandwiched between the exterior members 40, and the outer edge portions of the exterior members 40 are sealed and sealed by thermal fusion or the like. At that time, the adhesion film 41 is inserted between the positive electrode lead 31 and the negative electrode lead 32 and the exterior member 40. Thereby, the secondary battery shown in FIGS. 3 and 4 is completed.

  This secondary battery operates in the same manner as any one of the first to fourth embodiments, and has the same effect as any one of the first to fourth embodiments.

  Further, specific embodiments of the present invention will be described in detail.

(Examples 1-1 to 1-10)
A coin-type secondary battery as shown in FIG. 5 was produced. In this secondary battery, a positive electrode 51 and a negative electrode 52 are stacked via a separator 53 and sealed between an outer can 54 and an outer cup 55.

First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a ratio of Li ₂ CO ₃ : CoCO ₃ = 0.5: 1 (molar ratio), and 5 ° C. at 900 ° C. in the air. After firing for a time, lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material was obtained. Next, 91 parts by mass of this lithium / cobalt composite oxide (LiCoO ₂ ), 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Thereafter, the mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to a positive electrode current collector 51A made of an aluminum foil having a thickness of 20 μm, dried, and then compression molded to form a positive electrode active material layer 51B. After that, the positive electrode 51 was produced by punching into a pellet having a diameter of 15.5 mm.

  Moreover, 50 g of copper powder and 50 g of tin powder were mixed, this mixture was put into a quartz boat, heated to 1050 ° C. in an argon gas atmosphere, and allowed to cool to room temperature. The lump thus obtained was pulverized and classified in a ball mill for 30 minutes in an argon gas atmosphere to obtain a copper-tin (Cu-Sn) alloy powder. The average particle diameter of the obtained copper-tin alloy powder was measured with a laser diffraction particle size distribution measuring instrument (manufactured by Horiba Seisakusho) and found to be 10 μm. Then, using this copper-tin alloy powder as a negative electrode active material, 54.5 parts by mass of copper-tin alloy powder, 35 parts by mass of artificial graphite, 0.5 parts by mass of acetylene black as a conductive agent, and a binder A negative electrode mixture was prepared by mixing 10 parts by mass of polyvinylidene fluoride, and then dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a negative electrode mixture slurry. Next, the negative electrode current collector 52A made of copper foil was applied and dried, and then compression molded to form a negative electrode active material layer 52B. After that, it was punched into a pellet having a diameter of 15.5 mm to produce a negative electrode 52.

Furthermore, LiPF ₆ as an electrolyte salt is added to an equal volume mixed solvent of ethylene carbonate and diethyl carbonate so as to be 1 mol / l, and further difluorobenzene, trifluorobenzene, tetrafluorobenzene or pentafluorobenzene is added to perform electrolysis. A liquid was prepared. In that case, in Example 1-1, 1,2-difluorobenzene, in Example 1-2, 1,3-difluorobenzene, in Example 1-3, 1,4-difluorobenzene, in Example 1-4, 1, 2,3-trifluorobenzene, 1,2,4-trifluorobenzene in Example 1-5, 1,3,5-trifluorobenzene in Example 1-6, 1,2,4 in Example 1-7 3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene in Example 1-8, 1,2,4,5-tetrafluorobenzene in Example 1-9, and in Example 1-10 Pentafluorobenzene was used.

  Next, after laminating a negative electrode 52 and a separator 53 made of a microporous polypropylene film having a thickness of 30 μm in this order on the outer cup 55, injecting an electrolytic solution from above, and covering the outer can 54 containing the positive electrode 51, A coin-type secondary battery having a diameter of 20 mm and a height of 2.5 mm was manufactured by caulking the peripheral portions of the outer cup 55 and the outer can 54 with a gasket 56.

  Further, as Comparative Example 1-1 with respect to Examples 1-1 to 1-10, except that an electrolytic solution not containing difluorobenzene, trifluorobenzene, tetrafluorobenzene and pentafluorobenzene was used, and Comparative Example 1 -2, except that an electrolytic solution containing hexafluorobenzene was used, and coin-type secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-10.

  For the fabricated secondary batteries of Examples 1-1 to 1-10 and Comparative Examples 1-1 and 1-2, charging and discharging were performed for two cycles, the battery was disassembled, and difluorobenzene, trifluorobenzene, Tetrafluorobenzene and hexafluorobenzene contents were measured. The results are shown in Table 1.

  Charging / discharging was performed as follows. First, in a 20 ° C. environment, 1 mA constant current and constant voltage charge is performed up to an upper limit voltage of 4.2 V, then 1 mA constant current discharge is performed up to a final voltage of 2.5 V, and two cycles are performed under the same charge and discharge conditions. It was.

  In addition, initial capacity and cycle characteristics of the secondary batteries of Examples 1-1 to 1-10 and Comparative Examples 1-1 and 1-2 produced separately were measured. The obtained results are shown in Table 1.

  The initial capacity was calculated by charging and discharging under the above conditions. The cycle characteristics were obtained by charging and discharging under the above conditions and determining the capacity retention rate (%) at the 100th cycle when the discharge capacity at the first cycle was 100.

  As can be seen from Table 1, according to Examples 1-1 to 1-10 using the electrolytic solution containing difluorobenzene, trifluorobenzene, tetrafluorobenzene or pentafluorobenzene, the electrolytic solution not containing these was used. The initial capacity and the capacity retention rate were higher than those of Comparative Example 1-1 and Comparative Example 1-2 using an electrolytic solution containing hexafluorobenzene.

  That is, if the electrolyte contains difluorobenzene, trifluorobenzene, tetrafluorobenzene, or pentafluorobenzene, the anode material capable of occluding and releasing lithium is a simple element or alloy of a metal element or metalloid element. Alternatively, it was found that the cycle characteristics can be improved while maintaining a high capacity when the compound is contained.

(Examples 2-1 to 2-5)
A coin-type secondary battery was fabricated in the same manner as in Example 1-5 except that the content of 1,2,4-trifluorobenzene in the electrolytic solution was changed. For these secondary batteries, the content of 1,2,4-trifluorobenzene, the initial capacity and the capacity retention rate were determined in the same manner as in Example 1-5. The obtained results are shown in Table 2 together with the results of Example 1-5. FIG. 6 shows the relationship between the content of 1,2,4-trifluorobenzene and the capacity retention rate.

  As can be seen from Table 2 and FIG. 6, the initial capacity and the capacity retention rate increased as the content of 1,2,4-trifluorobenzene increased, and decreased after showing the maximum value.

  That is, it has been found that it is effective if the content of difluorobenzene, trifluorobenzene, tetrafluorobenzene or pentafluorobenzene is 0.0001 mass% or more and 0.1 mass% or less.

(Examples 3-1 to 3-3)
LiPF ₆ as an electrolyte salt is added to an equal volume mixed solvent of ethylene carbonate and diethyl carbonate so as to be 1 mol / l, and 1,3-difluorobenzene and 1,2,4-trifluorobenzene, or 1, Other than using 4-difluorobenzene and 1,2,4-trifluorobenzene, or an electrolyte containing 1,2,4-trifluorobenzene and 1,3,5-trifluorobenzene. Coin-type secondary batteries were produced in the same manner as in Examples 1-1 to 1-10. Also for these secondary batteries, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,4-trifluorobenzene and 1,3,5-similar to Examples 1-1 to 1-10. The content of trifluorobenzene, the initial capacity and the capacity retention rate were determined. The obtained results are shown in Table 3.

  As can be seen from Table 3, the same results as in Examples 1-1 to 1-10 were obtained. That is, it was found that the cycle characteristics can be improved even when the electrolytic solution contains two or more members selected from the group consisting of difluorobenzene, trifluorobenzene, tetrafluorobenzene, and pentafluorobenzene.

(Examples 4-1 to 4-3)
A negative electrode mixture was prepared by mixing 95 parts by mass of graphite as a negative electrode active material and 5 parts by mass of polyvinylidene fluoride as a binder, and this negative electrode mixture was added to N-methyl-2-pyrrolidone as a solvent. After being dispersed to form a negative electrode mixture slurry, it is uniformly applied to a negative electrode current collector 52A made of copper foil, dried, and compression-molded with a roll press to form a negative electrode active material layer 52B having a diameter of 15.5 mm. A coin-type secondary battery was fabricated in the same manner as in Examples 1-5, 2-1 to 2-5, except that the anode 52 was fabricated by punching into a pellet.

  As Comparative Example 4-1 with respect to Examples 4-1 to 4-3, except that an electrolytic solution not containing 1,2,4-trifluorobenzene was used, the rest was the same as in Examples 4-1 to 4-3. Similarly, a secondary battery was produced.

  The secondary batteries of Examples 4-1 to 4-3 and Comparative Example 4-1 were also subjected to 1,2,4-trimethyl electrolyte in the same manner as in Examples 1-5 and 2-1 to 2-5. The fluorobenzene content, initial capacity and cycle characteristics were measured. Table 4 shows the obtained results. FIG. 7 shows the relationship between the content of 1,2,4-trifluorobenzene and the capacity retention rate.

  As can be seen from Table 4 and FIG. 7, according to Examples 4-1 to 4-3 using the electrolytic solution containing 1,2,4-trifluorobenzene, comparative examples using the electrolytic solution not containing this The initial capacity and the capacity maintenance rate were higher than those of 4-1.

  On the other hand, as can be seen from Table 1, Table 4, FIG. 6 and FIG. 7, the improvement effect of the initial capacity and the capacity retention rate by Example 4-2 is that of Example 1 using a copper-tin alloy as the negative electrode active material It was lower than 5.

  That is, if the electrolytic solution contains difluorobenzene, trifluorobenzene, tetrafluorobenzene or pentafluorobenzene, even when a carbon material is used as a negative electrode material capable of inserting and extracting lithium, the cycle It was found that the characteristics can be improved.

  In addition, the improvement effect of the initial capacity and the capacity retention ratio is found to be particularly high when a single element, alloy or compound of a metal element or metalloid element is used as a negative electrode material capable of occluding and releasing lithium. It was.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the embodiments and examples, and various modifications can be made. For example, in the above embodiments and examples, a battery using lithium as an electrode reactant has been described. However, other alkali metals such as sodium (Na) or potassium (K), or alkalis such as magnesium or calcium (Ca) are used. The present invention can also be applied to the case of using an earth metal or another light metal such as aluminum. At that time, for example, as described in the above embodiment, the negative electrode has a simple substance, an alloy and a compound of a metal element capable of inserting and extracting the electrode reactant as the negative electrode active material, and the electrode reactant. And at least one member selected from the group consisting of simple substances, alloys and compounds of metalloid elements that can be released, and the negative electrode capacity is a capacity component caused by the negative electrode active material inserting and extracting the electrode reactant. It can comprise so that it may contain.

  In addition, in the embodiments and examples described above, the secondary potential using an exterior member such as a cylindrical secondary battery and a laminate film will be specifically described, and in the above examples, a coin-type secondary battery will be described. Although the secondary battery has been described, the present invention can be similarly applied to a secondary battery having another shape such as a button type or a square shape, or a secondary battery having another structure such as a laminated structure. . Further, the present invention is not limited to the secondary battery but can be similarly applied to other batteries such as a primary battery.

It is sectional drawing showing the structure of the secondary battery which concerns on one embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body in the secondary battery shown in FIG. It is sectional drawing showing the structure of the secondary battery which concerns on other embodiment of this invention. It is sectional drawing showing the structure along the II line of the winding electrode body shown in FIG. It is sectional drawing showing the structure of the secondary battery which concerns on the Example of this invention. It is the figure showing the relationship between content of the fluorinated benzene in a battery produced in the Example, and a capacity maintenance rate. It is the figure showing the relationship between content of the fluorinated benzene in another battery produced in the Example, and a capacity maintenance rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disc board, 16 ... Heat sensitive resistance element, 17, 56 ... Gasket, 20, 30 ... Winding electrode body, 21 , 33, 51 ... positive electrode, 21A, 33A, 51A ... positive electrode current collector, 21B, 33B, 51B ... positive electrode active material layer, 22, 34, 52 ... negative electrode, 22A, 34A, 52A ... negative electrode current collector, 22B, 34B, 52B ... negative electrode active material layer, 23, 35, 53 ... separator, 24 ... center pin, 25, 31 ... positive electrode lead, 26, 32 ... negative electrode lead, 36 ... electrolyte layer, 37 ... protective tape, 40 ... exterior member 41 ... Adhesion film, 54 ... Exterior can, 55 ... Exterior cup.

Claims (5)

  An electrolytic solution comprising at least one kind of fluorinated benzene selected from the group consisting of difluorobenzene, trifluorobenzene, tetrafluorobenzene and pentafluorobenzene.   2. The electrolytic solution according to claim 1, wherein the content of the fluorinated benzene is 0.0001% by mass or more and 0.1% by mass or less for each type of fluorinated benzene contained. A battery comprising an electrolyte solution together with a positive electrode and a negative electrode,
The battery characterized in that the electrolytic solution contains at least one kind of fluorinated benzene in the group consisting of difluorobenzene, trifluorobenzene, tetrafluorobenzene and pentafluorobenzene.   The battery according to claim 3, wherein the content of the fluorinated benzene in the electrolytic solution is 0.0001 mass% or more and 0.1 mass% or less for each of the fluorinated benzene contained. The negative electrode is at least one member selected from the group consisting of simple elements, alloys and compounds of metal elements and simple elements, alloys and compounds of metalloid elements as negative electrode active materials capable of inserting and extracting electrode reactants. The battery according to claim 3, comprising:

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